Synthesis of new C2-symmetrical bis(hydroxycamphorsulfonamide) ligands and their application in the enantioselective addition of dialkylzinc reagents to aldehydes and ketones

The preparation of several C-2-symmetric disulfonamides derived from chiral camphorsulfonyl chloride and different diamines (with or without stereogenic elements) is described. Their use in the titanium tetraisopropoxide-promoted enantioselective addition of dialkylzinc reagents to aldehydes has been tested, the best enantiomeric excess being up to 76%. Moreover, the unusual addition of dialkylzinc reagents to ketones can also be achieved with excellent enantioselectivity (up to 92% e.e.) using this type of ligand. When using para-substituted phenones as electrophiles, the enantiomeric excess of the resulting tert-alcohol is independent of the electronic properties of the group attached to the aromatic ring of the phenone. In the case of using more hindered ketones the enantioselectivity is lower, so indicating a steric influence in the reaction. (C) 2003 Elsevier Science Ltd. All rights reserved.